Daiane Boff

Pathogens have evolved to be highly adapted to their natural host. Community-associated methicillin-resistant Staphylococcus aureus USA300, for instance, is a lineage responsible for the epidemic of skin and soft tissue infections (SSTIs) in humans. Owing to its human tropism, mechanisms that enabled the rise of USA300 as a major skin pathogen remain incompletely defined. By leveraging a rodent-adapted strain of S. aureus , we developed a natural model of SSTIs. We found that LukMF′, a pore-forming leukocidin homolog to the human-specific LukSF-PV toxin, drives skin pathology in mice. LukMF′ lyses neutrophils via the chemokine receptor CCR1, which in turn fuels inflammatory pathology and microbial survival within the infectious nidus. Ablation of CCR1, depletion of neutrophils, or vaccination with LukMF′ all protected mice from skin pathology. Thus, these data support epidemiological studies linking leukocidins with human SSTIs and highlight the power of natural models to unearth potential targets to curtail infections.

We recently described the evolution of a community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) USA300 variant responsible for an outbreak of skin and soft tissue infections. Acquisition of a mosaic version of the Φ11 prophage (mΦ11) that increases skin abscess size was an early step in CA-MRSA adaptation that primed the successful spread of the clone. The present report shows how prophage mΦ11 exerts its effect on virulence for skin infection without encoding a known toxin or fitness genes. Abscess size and skin inflammation were associated with DNA methylase activity of an mΦ11-encoded adenine methyltransferase (designated pamA ). pamA increased expression of fibronectin-binding protein A ( fnbA ; FnBPA), and inactivation of fnbA eliminated the effect of pamA on abscess virulence without affecting strains lacking pamA . Thus, fnbA is a pamA -specific virulence factor. Mechanistically, pamA was shown to promote biofilm formation in vivo in skin abscesses, a phenotype linked to FnBPA’s role in biofilm formation. Collectively, these data reveal a novel mechanism—epigenetic regulation of staphylococcal gene expression—by which phage can regulate virulence to drive adaptive leaps by S. aureus . Graphical